Large capacity rechargeable batteries are currently being investigated for use in electric vehicles. The ultimate feasibility of electric vehicles depends on significantly reducing the associated costs. Reduction in the costs of battery assemblies is particularly important. Lithium ion batteries are an important type of battery technology.
Most battery assemblies, including lithium ion battery assemblies, include a plurality of individual electrochemical cells. FIG. 1A provides a schematic cross section of an electrochemical cell that is used in many prior art battery assemblies. Electrochemical cell 10 includes anode 12 and cathode 14. Typically, anode 12 includes a metal sheet or foil 16 (usually copper metal) over-coated with graphitic layer 18. Similarly, cathode 14 includes metal sheet or foil 20 (usually aluminum metal) over-coated with a lithium-containing layer 22. Finally, electrochemical cell 10 includes electrolyte 24 which is interposed between anode 12 and cathode 14. Terminals 26 and 28 allow the generated electricity to be used in an external circuit.
Electrochemical cells produce electricity via an electrochemical reaction. In the case of lithium ion battery cells, an example of the electricity generating reactions are described by the following formulae:Cathode Reaction: LiMO2Li1-xMO2+xLi++xeAnode Reaction: C+xLi++xeLixCOverall Reaction: LiMO2+CLixC+Li1-xMO2 where LiMO2 is a lithiated transition metal oxide. Other materials may be used as a cathode and anode of a li-ion cell, resulting in different electricity generating reactions.
The reactions occurring in a lithium ion battery cell are reversible, thereby providing the ability of such cells to be recharged. During battery discharge, the anode provides electrons to an external circuit and lithium ions to the electrolyte from lithium that is intercalated within the graphitic coating on the anode. During charging the movement of the lithium ions is reversed.
FIG. 1B provides a schematic cross section of a prior art battery assembly that includes a plurality of electrochemical cells. Battery assembly 30 includes electrochemical cells 32-56 which are of the basic design set forth in FIG. 1A. In this design, active elements of the internal electrodes (anode or cathode) are deposited on both sides of current carriers 58, 59. Moreover, in accordance with this design the electrochemical cells are arranged in a parallel configuration with the anodes of each cell electrically connected together and the cathodes of each cell electrically connected together. Thus the voltage generated between the electrodes of the battery assembly 30 is the same as the voltage generated between the electrode of the battery assembly 10.
FIG. 1C provides a schematic cross section of a prior art battery assembly formed from a plurality of battery subassemblies arranged in a parallel configuration. Battery assembly 60 includes battery subassemblies 62-66 which are of the general design of the battery assembly set forth in FIG. 1B. In accordance with this design, the battery subassemblies are arranged in a parallel configuration with the anodes of each battery subassembly electrically connected together and the cathodes of each battery subassembly electrically connected together. Thus the voltage generated between the electrodes of the battery assembly 60 is the same as the voltage generated between the electrodes of the battery assembly 10 and the voltage generated between the electrodes of the battery assembly 30.
FIG. 1D provides a schematic cross section of a prior art battery assembly formed from a plurality of battery subassemblies arranged in a series configuration. Battery assembly 70 includes battery subassemblies 72-76 which are of the general design of the battery assembly set forth in FIG. 1B or in FIG. 1C. In accordance with this design, the battery subassemblies are arranged in series with the anode of a battery subassembly electrically connected to the cathode of the next battery subassembly.
Although the battery assemblies of FIGS. 1A-1D work reasonably well, improved designs that are easier to assemble are still desirable. In particular, there is a desire to decrease the costs associated with fabricating high capacity battery assemblies for automotive applications.
Accordingly, there is a need for battery assemblies of simpler design that are more economical that the current prior art assemblies.